Electric heater



H. INGRAM ELECTRIC HEATER Aug. 1, 1950 2 Sheets-Sheet 1 Filed ma 14,194v In venlor Him Emnvq I By M*@AA A ltorney 1950 H. INGRAM 2,517,110

ELECTRIC HEATER Filed May 14, 1947 2 Sheets-Sheet 2 145/?6 97 IA CK PMInventor A tlomey Patented Aug. 1, 1950 UNITED STATES PATENT OFFICEApplication May 14, 1947, Serial No. 747,892 In Great Britain May 18,1948 Claims. (Ci. 201-73) This invention relates to electric heaters orradiators for domestic and other purposes and has for its object toprovide an improved form of electric heater and method of constructingthe same.

According to the invention an electric heater or radiator ismanufactured by forming an electrio resistance element wherein the coilsor turns of wire are maintained in interspaced relationship, by totallyenclosing the said element within a body of insulating material, bysubjecting the said body to treatment by pressure and heat whereby theinsulating material is caused to bond between the coils or turns of wirewhich are thereby completely embedded within the hardened body resultingfrom the heat treatment, and by subsequently providing the embedded wireor wires with means for connection to a source of electrical powersupply.

The insulating material employed is of a character which will harden andform a homogeneous body under heat treatment and be sufiiclentlyresistant to heat to remain unaffected byoperation as a heamr. Asuitable insulating material for the purpose consists of a vitreous bodyin which iinely divided mica and/or other dielectric materials aredispersed. In particular the insulating material employed is a micaceousinsulating material formed by mixing low fusing point vitreous materialwith powdered mica and heating the mixture so that the mica is bonded tothe vitreous material at a temperature below the point or totaldehydration. 'l'he resulting product (which can be sewn, drilled orotherwise tooled) is a material resembling slate in appearance and whichhas a tensile strength considerably in excess of that of other porcelainor plastic insulators. This mica insulating material therefore is not tobe confused with the concrete material 01' Miller (U. S. Patent No.2,408,149, September 24, 1946) or the plastic material of Megow (U. S.Patent No. 2,302,256, November 17, 1942) and gives rise to the problemhow to insert the electrical heating element for correct positioningwithin the mica material and to maintain the heating element in theexact position required during the subsequent stages of pressing andheating the material.

Reference will now be made to the accompanying drawings which illustratethe manufacture of an electric heater according to the inven- Fig. 2 isa fragmentary perspective view on an enlarged scale showing one of theterminal pads.

Fig. 3 is a detail sectional view on an enlarged scale showing onemethod of attaching an electrical terminal, and

Fig. 4 is a view of a completed heater.

In carrying the invention into effect an electric heater or radiator isconstructed by first forming the heating element shown in Fig. 1. Thisis enacted by winding resistance wire a on to a cardboard former inwhich is of rectilineal form and has a number (conveniently four) ofrectangular ventilation apertures 0 cut in equispaced positions withinit.

The'cardboard former b is also formed with an elongated central slot dwhose longer edges are recessed to form two series or lugs 6. Similarlugs j are formed by recessing those outer edges of the former which areparallel to the longer edges of the slot 12. The lugs j occupy positionscorresponding to the recesses between the lugs e. The two series of lugse and I enable the wire a to be wound in two serles of turns, as shownin Fig. l, the turns being maintained in their correct interspacedrelationship by the loop at the end of each pair or turns passing aroundone of the lugs. The stretch Of wire which passes at 9 completely acrossone end of the former is retained against displacement by passing itsmidportion through two notches it cut in the adjacent edge of theformer.

At the end of the former remote from the notches h, the ends of the Wirea are connected to terminal pads constructed as shown more clearly inFig. 2. These terminal pads consist of thin copper plates 2. secured tothe former by wire staples a or any other convenient means. To preventdisplacement or the end portions of the wire they are threaded throughapertures la in the former and their ends are secured to the plates i bydouble folding one edge 1 of each over the wire and pressing flat. Thecurves m or the plates 1' are bent at right angles to the main portionsof the plates to anchor the plates securely in the insulating materialwhich is subsequently formed around the wire assembly. The former withthe wire winding arranged secured as above described is embedded withina body of mlcaceous insulating materlal prepared as aoove described andwhile this material is still in the finely divided form the wire woundformer is positioned between two layers of the material in a press. Thematerial is then pressed in the cold state, resulting in the productionof a rectangular plate of a thickness which may be of the order of halfan inch. This plate is then allowed to dry at room temperature. Afterdrying the plates are subjected to heat treatment in a furnace, thefirst result of which is to disintegrate the cardboard former, theairspaces c in the former allowing sufllcient air to be trapped withinthe pressed plate for the cardboard former to be substantiallycompletely consumed but in order that as little residue as possibleshall remain, it is preferable to use for the purpose a cardboard with ahigh carbon content such as strawboard.

After furnace treatment the plate is subjected to a hot pressingoperation for a short period which corrects any tendency to warp andensures that the'sp'ace initially occupied by the former is filled bythe mlcaceous material which is thereby caused to bond between thewindings of resistance wire a, which are maintained in their initialrelative positions shown in Fig. l.

in air. The edges are then ground to remove any unevenness which mayhave resulted from the pressing operation and the heater 1: having theform shown in Fig. 3. is then ready for use after connection thereto ofelectrical conductors.

This invention includes means other than that above described forpositioning the electrical heating element or elements within amicaceous insulating plate, For example, instead of using a cardboardformer a meshwork can be prepared in which stiff threads reinforced withasbestos constitute the warp while the weft is constituted by nickelchrome wire which is afterwards to form the resistance element. Thismeshwork is embedded in the micaceous powder and the heater completed inthe manner already described, the meshwork allowing the insulatingmaterial to bond between the wires.

According to another form of the invention, the resistance element isconstructed by looping the resistance wire around two series of pins orstuds mounted in a fixed support, the loops being laid on gummed paperand when the wire arrangement is completed a further sheet of paper islaid on the assembly and caused to adhere to the first sheet with theends of the wire loops projecting around the edges. assembly to bewithdrawn from the pins and inserted within the micaceous powder asbefore, the paper retaining the wire turns in correct relative positionsduring the initial pressure application but being disintegrated by theheat treatment. The adhesive used in this form of the invention must notcontain gelatine or any like substance which may be inert to the heattreatment.

In all the forms above described it is necessary to provide forelectrically connecting external conductors to the embedded resistanceelement. After completion of the heater. the plate 11. is tapped and aknurled brass plug (Fig. 3) is inserted into the hole :2, which extendsthrough the copper plate i and enables electrical connection to beestablished. The plug 0 may be provided with a screw threaded socket qto receive a screw and nut of any usual form, or the plug 0 may beformed integral with a screw-threaded stud. Alternatively, a springpressed plug can be loosely inserted in the tapped hole 9 and held inposition by a cover which is screwed in position adjacent one edge ofthe heater plate in such a.

manner as to screen completely the electrical connecting means. In thecompleted heater After the heating and subsequent hot pressure operationthe plate is allowed to cool and is dried This enables the a surface orsurfaces may be moulded with designs during the final heat pressingoperation or it may be painted by the use of distemper or other oillesspaint. Where a very dark colour is required certain dark oil-boundpaints can be used and if a copper shield is embedded on or in themoulded material certain light oil-bound paints can be used fordecoration. Such copper sheet, however, would always have to becompletely insulated from the wire resistance element a.

To use a heater as above described it is preferably mounted in slottedmetal columns 1' (Fig. 4) provided with feet 8 so that the plate noccupies a vertical position. The structure is completed by a handle 12to enable the heater to be carried from one position to another.Alternatively, the plate can be suspended or otherwise supported in ahorizontal or inclined position according to the.

particular purpose for which it is to be employed. For example, a plate11. formed as described may be used as a heating panel disposed in arecess in a wall or partition.

In addition to the above uses, the heater plates can be utilised indrying cupboards, incubators and chicken brooders for attachment to ornear water pipes and tanks to prevent freezing, or for temperatureraising: for vehicle heating and to prevent freezing in cooling system,either by attachment to or insertion in a suitable position on thevehicle, or by placing on the floor beneath the engine: for defrostingautomobile windscreens or shop and other windows, and for prevention ofmoisture formation on radio and other apparatus. The plates may also beused in a horizontal position as a warming plate for chemical,industrial and domestic vessels, and as the heating plate in aphotographic print dryer or glazer. Further, the plates may besurrounded by a metal shield for decorative purposes or to produce aheater which is flameproof for use in mines or in other inflammableatmospheres.

With lower wattage loadings and hence surface temperatures, they may beutilised for soil heating and other purposes where moderate heat andimmunity from the efiects of damp and erosion are essential.

I claim:

1. The method of manufacturing an electric heater or radiator with anelectric wire resistance element embedded and totally enclosed within abody of insulating material, which comprises winding the electric wireresistance over a slotted destructible former provided with definedlocations adapted for engagement by the wound wire to maintain the wirein a predetermined configuration, embedding the thus wound former withina mass of the insulating material in a finely divided or particlecondition, the said material being susceptible to heat and pressure tobond and set the particles into a homogeneous whole constituting theheater body part, and subjecting the said mass, with the wire woundformer therein, to heat and pressure to disintegrate the former andleave the wire bonded to the interior of the ultimately set and hardenedbody part.

2. The method of manufacturing an electric heater or radiator accordingto claim 1 wherein the ends of the-resistance wire are connected tometallic terminal pads attached to the former and adapted to receiveterminal plugs or sockets after the moulding of the insulating materialhas been completed.

3. The method of manufacturing an electric heater or radiator accordingto claim 1 wherein the said former comprises a rectangular sheet ofdestructible material having spaced apertures therein including acentral aperture and lugs formed along the edges of the said centralaperture and along the edges of the sheet parallel to the said centralaperture for the purpose of engaging and spacing the turns of resistancewire.

4. An electric surface heater comprising a main molded body part in theform of a fiat plate or slab, said body part being composed of amicaceous insulating material and including an electric resistanceelement, said element being completely enclosed and embedded in themolded body part in the form of substantially parallel straightstretches oi a continuous resistance wire, said wire having opposedterminal ends enclosed within said body part, electrical terminal padsalso completely embedded within the molded body part and connected withsaid terminal ends of the resistance wire, and electric coupling meanson said body part adapted for the connection of the electric powersupply to said electrical terminal pads.

5. A method of manufacturing an electric heater or radiator with anelectric wire resistance element embedded and totally enclosed within abody 01' micaceous insulating material, which comprises winding theelectric wire resistance over aformer having defined locations withwhich the wound wire is engaged and which serve to maintain the wire, ina predetermined configuration upon the former, connecting electricterminals to the ends of the resistance wire on the former, embeddingthe thus wound former and electric terminal carrier within a mass of theinsulating material in a finely divided or particle condition, the saidmaterial being susceptible to heat and pressure to bond and set theparticles into a homogeneous whole constituting the heater body part,subjecting the said mass, with the wire wound former therein, to heatand. pressure to leave the wire and electric terminais bonded to theinterior of the ultimately set andhardened body part, and securingelectric coupling means on the molded body part adapted for theconnection of the electric power supply to said electric terminals.

WERE INGRAM.

REFEBENEES @ITED The following references are of record in the ills ofthis patent:

UNITED STATES PATENTS Miller et al Sept. 24, 1946

